1. Field of the Invention
The invention relates to a motor control, and more particularly, to a signal processing method and apparatus for improving the speed and the position resolutions of an encoder output signal when the motor control is performed using an analog output encoder.
2. Description of the Related Art
In conventional ink jet imaging apparatuses, a recording medium is carried therein using at least one feed roll along a carry path. To form an image accurately on the recording medium, the recording medium must be placed at a specific location. To position the recording medium at the specific location, the feed roll must move with high precision. Hence, the quality of an image is often very dependent upon precise control of the position of the feed roll. An encoder is typically used to precisely control the position of a feed roll.
An encoder typically uses at least one sensor to sense slits that are position marks and formed along the track of a code wheel, for example, a disk. Preferably, the code wheel has a central shaft in alignment with the central shaft of a feed roll and rotates with a rotation of the feed roll. When the code wheel rotates, the number of slits by which the sensor and its accompanying elements pass is counted. Since each of the slits indicates movement of the code wheel at a predetermined angle, changes in the position of the recording medium carried by the feed roll can be tracked.
A square-wave pulse encoder cannot obtain distinct position information between rising and falling edges of a square-wave pulse output by the encoder. Hence, an analog output encoder is used because fine position information can be obtained even during one cycle by finely dividing the angles of rotation of a motor by analog values. To increase a resolution of an analog output encoder, a code wheel is enlarged, or the interval between adjacent slits is reduced. However, if the code wheel is enlarged, the analog output encoder becomes large and bulky. If the interval between adjacent slits is reduced, an encoder output signal is highly likely to be unstabilized due to the characteristics of the electrical circuit of a sensor, the sensitivity of the sensor, and the mechanical and optical characteristics of the code wheel.
Also, to increase the resolution of an analog output encoder, a signal processing circuit is used, in which a sinusoidal signal output by the analog output encoder is divided into 2n sections according to the resolution of analog-to-digital conversion, that is, according to the number of bits, n, and an instantaneous value is read out from each of the 2n sections so that analog-to-digital conversion is performed. However, in this method, numerical errors and jitters often occur on the curve of the sinusoidal signal due to the characteristics of the sinusoidal signal in that only about π/4 of a half-period maintains linearity, and, accordingly, a processor using an analog-to-digital converted signal cannot precisely control the location or speed of a recording medium. Also, because the sections sequentially undergo the analog-to-digital conversion, delay time is generated, and a load on the processor increases. Such problems adversely affect other signal processing operations performed in the processor.